⚡ Optimize FileAuditStore::log_async to use spawn_blocking

[Tuntii]

Refactored FileAuditStore to use an Arc<Inner> internal structure, enabling cheap cloning.
Implemented log_async using tokio::task::spawn_blocking to offload synchronous file I/O to the blocking thread pool, preventing async runtime stalls.
Preserved synchronous log behavior for non-async contexts.

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PR created automatically by Jules for task 14806398196114527397 started by @Tuntii

[google-labs-jules]

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[Copilot]

Pull request overview

This PR optimizes the FileAuditStore implementation to better support async contexts by preventing async runtime stalls. The refactoring introduces an Arc<Inner> pattern that enables cheap cloning while maintaining shared internal state, and implements log_async using tokio::task::spawn_blocking to offload synchronous file I/O operations to a dedicated thread pool.

Changes:

• Refactored internal structure to use Arc<FileAuditStoreInner> pattern for efficient cloning
• Implemented log_async with tokio::task::spawn_blocking to prevent async runtime blocking
• Added Clone and Debug trait implementations to FileAuditStore

[Copilot]

The new log_async method lacks test coverage. Given that the codebase uses comprehensive async testing (as seen in other modules like replay, api_key, circuit_breaker, etc.), and that log_async introduces new behavior with spawn_blocking, it should have dedicated test coverage. Consider adding a test like:

#[tokio::test]
async fn test_file_store_log_async() {
let (store, _dir) = temp_store();
let event = AuditEvent::new(AuditAction::Create).actor("admin");
let id = event.id.clone();
store.log_async(event).await.unwrap();
store.flush().unwrap();
let retrieved = store.get(&id).unwrap();
assert!(retrieved.is_some());
}

This would verify that the spawn_blocking mechanism works correctly and that events logged asynchronously are properly persisted.